Small electronic devices composed by mounting a plurality of circuit components on a wiring board have been rapidly finding wide application in recent years. Such conventional technology is disclosed, for example, in JP-A-11-163583, JP-A-2001-24312, and JP-A-2001-168493.
FIG. 8 shows a conventional circuit component built-in module 10 (referred to hereinbelow as a module). As shown in FIG. 8, a circuit pattern 11 and electrodes 30 are formed on the front surface of a wiring board 20 and then covered with a solder resist 60. Then, a circuit component 40 and electrodes 30 are connected with a solder 50. The surface of the wiring board 20 is then covered with an insulating resin 70 so as to enclose the circuit component 40. Finally, a module is obtained by providing an electromagnetic shielding layer 15 obtained by metal plating on the outermost layer. The wiring board 20 comprises an inner via 80, an internal circuit pattern 12, rear surface electrodes 13, and a solder 14 provided on the rear surface electrodes 13. Thus, the conventional module has a configuration in which the circuit component 40 and wiring board 20 are connected with the solder 50 and covered from above with the insulating resin 70.
On the other hand, in contemporary miniature circuit components with a size of 1.0×0.5 mm or 0.6×0.3 mm, the quantity of applied solder is reduced in order to avoid solder short circuiting during mounting. For this reason, a gap between the circuit component 40 and wiring board 20 after mounting is merely about 10 μm, and when the insulating resin 70 is formed, the insulating resin 70 cannot sufficiently penetrate into the gap portion between the circuit component 40 and wiring board 20 and a cavity appears therein. If the module and a motherboard are soldered together in a state in which a cavity appeared between the circuit component 40 and wiring board 20, the solder 50 is remelted inside the module. This molten solder 50 then flows out into the gap portion between the circuit component 40 and wiring board 20. As a result, short circuit occurs between the electrodes 30 and impairs the functions of the module. A method has been suggested for preventing the solder 50 from remelting inside the module when the module is mounted on the motherboard. With this method, a high-melting solder with a melting point of higher than 280° C. is used as the material for the solder 50, and the gap portion between the circuit component 40 and wiring board 20 is filled with an insulating resin by vacuum printing.
However, a process conducted at a temperature of 280° C. or higher is required when the circuit component 40 is mounted on the wiring board 20. Accordingly, the problem is that materials with low heat resistance, for example, quartz components and wiring boards composed of resins cannot be used for the circuit component 40 and wiring board 20 employed in the module.
The present invention resolves the above-described problems of the related art and provides a circuit component built-in module which has excellent connection reliability.